Signaling sub-prediction unit motion vector predictor

ABSTRACT

A method of decoding video data comprising parsing a sub-prediction unit motion flag from received encoded video data, deriving a list of sub-prediction unit level motion prediction candidates if the sub-prediction unit motion flag is active, deriving a list of prediction unit level motion prediction candidates if the sub-prediction unit motion flag is not active, and decoding the encoded video data using a selected motion vector predictor.

This application claims the benefit of U.S. Provisional Application No. 62/687,052, filed Jun. 19, 2018, the entire content of which is incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard, ITU-T H.265/High Efficiency Video Coding (HEVC), and extensions of such standards. The video devices may transmit, receive, encode, decode, and/or store digital video information more efficiently by implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.

SUMMARY

In general, this disclosure relates to motion vector prediction in video codecs. For example, a motion vector predictor is selected adaptively from two lists of motion vector prediction candidates, which are derived. The first list includes PU level motion vector prediction candidates, the second list includes sub-PU level motion vector prediction candidates.

In one example embodiment, a method of decoding video data is discussed.

The method includes receiving encoded video data, parsing a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, deriving a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, deriving a list of prediction unit level motion prediction candidates, selecting a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decoding the encoded video data using the selected motion vector predictor. The encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block. The neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture. The list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks. Pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor. The prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates. The list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD). The method includes deriving a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.

In another example embodiment, an apparatus for decoding video data is discussed. The apparatus includes a memory for storing a received encoded video data and a processor. The processor configured to parse a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, derive a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, derive a list of prediction unit level motion prediction candidates, select a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decode the encoded video data using the selected motion vector predictor. The encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block. The neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture. The list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks. Pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor. The prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates. The list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD). The processor further configured to derive a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.

In another example embodiment, an apparatus for decoding video data is discussed. The apparatus includes a memory means for storing a received encoded video data and a processor means. The processor means configured to, parse a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, derive a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, derive a list of prediction unit level motion prediction candidates, select a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decode the encoded video data using the selected motion vector predictor. The encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block. The neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture. The list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks. Pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor. The prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates. The list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD). The processor means is further configured to derive a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.

In another example embodiment, a non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform a method. The method includes receiving encoded video data, parsing a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, deriving a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, deriving a list of prediction unit level motion prediction candidates, selecting a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decoding the encoded video data using the selected motion vector predictor. The encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block. The neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture. The list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks. Pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor. The prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates. The list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD). The method includes deriving a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtree binary tree (QTBT) structure, and a corresponding coding tree unit (CTU).

FIG. 3 is a flow chart illustrating motion vector predictor derivation.

FIG. 4 is a conceptual diagram illustrating spatial neighboring motion vector candidates for a merge mode.

FIG. 5 is a conceptual diagram illustrating temporal motion vector candidates.

FIG. 6 illustrates candidate motion vector blocks selection techniques.

FIG. 7 is a conceptual diagram illustrating of Spatial-Temporal Motion Vector Prediction (STMVP).

FIG. 8 is a conceptual diagram illustrating bilateral matching techniques.

FIG. 9 is a conceptual diagram illustrating template matching techniques.

FIG. 10 is a conceptual diagram illustrating planar motion vector prediction.

FIG. 11 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

FIG. 12 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

DETAILED DESCRIPTION

This disclosure is related to decoder-side motion vector derivation (DMVD). The decoder-side motion vector derivation techniques described in this disclosure may be used in conjunction with any of the existing video codecs, such as HEVC (High Efficiency Video Coding), or may be used as coding techniques for any future video coding standards, such as H.266 Versatile Video Coding (VVC) and Essential Video Coding (EVC).

FIG. 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of this disclosure. The techniques of this disclosure are generally directed to coding (encoding and/or decoding) video data, and in particular, are related to techniques discussed herein. In general, video data includes any data for processing a video. Thus, video data may include raw, uncoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116, in this example. In particular, source device 102 provides the video data to destination device 116 via a computer-readable medium 110. Source device 102 and destination device 116 may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such smartphones, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device 102 and destination device 116 may be equipped for wireless communication, and thus may be referred to as wireless communication devices.

In the example of FIG. 1, source device 102 includes video source 104, memory 106, video encoder 200, and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120, and display device 118. In accordance with this disclosure, video encoder 200 of source device 102 and video decoder 300 of destination device 116 may be configured to apply the techniques for decoder-side motion vector derivation. Thus, source device 102 represents an example of a video encoding device, while destination device 116 represents an example of a video decoding device. In other examples, a source device and a destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source, such as an external camera. Likewise, destination device 116 may interface with an external display device, rather than including an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, any digital video encoding and/or decoding device may perform techniques for decoder-side motion vector derivation. Source device 102 and destination device 116 are merely examples of such coding devices in which source device 102 generates coded video data for transmission to destination device 116. This disclosure refers to a “coding” device as a device that performs coding (encoding and/or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of coding devices, in particular, a video encoder and a video decoder, respectively. In some examples, devices 102, 116 may operate in a substantially symmetrical manner such that each of devices 102, 116 include video encoding and decoding components. Hence, system 100 may support one-way or two-way video transmission between video devices 102, 116, e.g., for video streaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e., raw, uncoded video data) and provides a sequential series of pictures (also referred to as “frames”) of the video data to video encoder 200, which encodes data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 encodes the captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the pictures from the received order (sometimes referred to as “display order”) into a coding order for coding. Video encoder 200 may generate a bitstream including encoded video data. Source device 102 may then output the encoded video data via output interface 108 onto computer-readable medium 110 for reception and/or retrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memories. In some example, memories 106, 120 may store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106, 120 may store software instructions executable by, e.g., video encoder 200 and video decoder 300, respectively. Although shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memories for functionally similar or equivalent purposes. Furthermore, memories 106, 120 may store encoded video data, e.g., output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106, 120 may be allocated as one or more video buffers, e.g., to store raw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or device capable of transporting the encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium to enable source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a radio frequency network or computer-based network. Output interface 108 may modulate a transmission signal including the encoded video data, and input interface 122 may modulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data to file server 114 or another intermediate storage device that may store the encoded video generated by source device 102. Destination device 116 may access stored video data from file server 114 via streaming or download. File server 114 may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device 116. File server 114 may represent a web server (e.g., for a website), a File Transfer Protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. Destination device 116 may access encoded video data from file server 114 through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to a streaming transmission protocol, a download transmission protocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wireless transmitters/receiver, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 comprise wireless components, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In some examples where output interface 108 comprises a wireless transmitter, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. In some examples, source device 102 and/or destination device 116 may include respective system-on-a-chip (SoC) devices. For example, source device 102 may include an SoC device to perform the functionality attributed to video encoder 200 and/or output interface 108, and destination device 116 may include an SoC device to perform the functionality attributed to video decoder 300 and/or input interface 122.

The techniques of this disclosure may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded video bitstream from computer-readable medium 110 (e.g., non-transitory storage device 112, file server 114, or the like). The encoded video bitstream computer-readable medium 110 may include signaling information defined by video encoder 200, which is also used by video decoder 300, such as syntax elements having values that describe characteristics and/or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like). Display device 118 displays decoded pictures of the decoded video data to a user. Display device 118 may represent any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 and video decoder 300 may each be integrated with an audio encoder and/or audio decoder, and may include appropriate MUX-DEMUX units, or other hardware and/or software, to handle multiplexed streams including both audio and video in a common data stream. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as any of a variety of suitable encoder and/or decoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 200 and video decoder 300 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device. A device including video encoder 200 and/or video decoder 300 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multi-view Video Coding (MVC) extensions.

A video coding standard, namely High Efficiency Video Coding (HEVC) or ITU-T H.265, including its range extension, multiview extension (MV-HEVC) and scalable extension (SHVC), has been developed by the Joint Collaboration Team on Video Coding (JCT-VC) as well as Joint Collaboration Team on 3D Video Coding Extension Development (JCT-3V) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studying the potential need for standardization of future video coding technology with a compression capability that exceeds that of the current HEVC standard (including its current extensions and near-term extensions for screen content coding and high-dynamic-range coding). The groups are working together on this exploration activity in a joint collaboration effort known as the Joint Video Exploration Team (JVET) to evaluate compression technology designs proposed by their experts in this area. The JVET first met during 19-21 Oct. 2015. And the latest version of reference software, i.e., Joint Exploration Model 7 (JEM 7) could be downloaded from: https://jvet.hhi.fraunhofer.de/svn/svn_HMJEMSoftware/tags/HM-16.6-JEM-57.0/An Algorithm description of Joint Exploration Test Model 7 (JEM7) could be referred to JVET-G1001.

Video encoder 200 and video decoder 300 may operate according to a video coding standard, such as ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC) or extensions thereto, such as the multi-view and/or scalable video coding extensions. Alternatively, video encoder 200 and video decoder 300 may operate according to other proprietary or industry standards, such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also referred to as Versatile Video Coding (VVC). A recent draft of the VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 3),” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13th Meeting: Marrakech, Mass., 9-18 January 20190, JVET-M1001-v3 (hereinafter “VVC Draft 4). The techniques of this disclosure, however, are not limited to any particular coding standard.

As will be discussed, video decoder 300 may be configured to perform one or more techniques of this disclosure. For example, video decoder 300 may parse a sub-prediction unit motion flag from received encoded video data, derive a list of sub-prediction unit level motion prediction candidates if the sub-prediction unit motion flag is active, derive a list of prediction unit level motion prediction candidates if the sub-prediction unit motion flag is not active, and decode the encoded video data using a selected motion vector predictor.

In general, video encoder 200 and video decoder 300 may perform block-based coding of pictures. The term “block” generally refers to a structure including data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and/or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and/or chrominance data. In general, video encoder 200 and video decoder 300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red, green, and blue (RGB) data for samples of a picture, video encoder 200 and video decoder 300 may code luminance and chrominance components, where the chrominance components may include both red hue and blue hue chrominance components. In some examples, video encoder 200 converts received RGB formatted data to a YUV representation prior to encoding, and video decoder 300 converts the YUV representation to the RGB format. Alternatively, pre- and post-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding and decoding) of pictures to include the process of encoding or decoding data of the picture. Similarly, this disclosure may refer to coding of blocks of a picture to include the process of encoding or decoding data for the blocks, e.g., prediction and/or residual coding. An encoded video bitstream generally includes a series of values for syntax elements representative of coding decisions (e.g., coding modes) and partitioning of pictures into blocks. Thus, references to coding a picture or a block should generally be understood as coding values for syntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder (such as video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four equal, non-overlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes without child nodes may be referred to as “leaf nodes,” and CUs of such leaf nodes may include one or more PUs and/or one or more TUs. The video coder may further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents partitioning of TUs. In HEVC, PUs represent inter-prediction data, while TUs represent residual data. CUs that are intra-predicted include intra-prediction information, such as an intra-mode indication.

As another example, video encoder 200 and video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, a video coder (such as video encoder 200) partitions a picture into a plurality of coding tree units (CTUs). Video encoder 200 may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure. The QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC. A QTBT structure of JEM includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) partitions. A triple tree partition is a partition where a block is split into three sub-blocks. In some examples, a triple tree partition divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use a single QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder 200 and video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luminance component and another QTBT or MTT structure for both chrominance components (or two QTBT/MTT structures for respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to use quadtree partitioning per HEVC, QTBT partitioning, or MTT partitioning or other partitioning structures. For purposes of explanation, the description of the techniques of this disclosure is presented with respect to QTBT partitioning. However, it should be understood that the techniques of this disclosure may also be applied to video coders configured to use quadtree partitioning, or other types of partitioning as well.

This disclosure may use “N×N” and “N by N” interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, e.g., 16×16 samples or 16 by 16 samples. In general, a 16×16 CU will have 16 samples in a vertical direction (y=16) and 16 samples in a horizontal direction (x=16) Likewise, an N×N CU generally has N samples in a vertical direction and N samples in a horizontal direction, where N represents a nonnegative integer value. The samples in a CU may be arranged in rows and columns. Moreover, CUs need not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, CUs may comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing prediction and/or residual information, and other information. The prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU. The residual information generally represents sample-by-sample differences between samples of the CU prior to encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, video encoder 200 may generate the prediction block using one or more motion vectors. Video encoder 200 may generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder 200 may calculate a difference metric using a sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or other such difference calculations to determine whether a reference block closely matches the current CU. In some examples, video encoder 200 may predict the current CU using uni-directional prediction or bi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensation mode, which may be considered an inter-prediction mode. In affine motion compensation mode, video encoder 200 may determine two or more motion vectors that represent non-translational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select an intra-prediction mode to generate the prediction block. Some examples of JEM and VVC provide sixty-seven intra-prediction modes, including various directional modes, as well as planar mode and DC mode. In general, video encoder 200 selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder 200 codes CTUs and CUs in raster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for a current block. For example, for inter-prediction modes, video encoder 200 may encode data representing which of the various available inter-prediction modes is used, as well as motion information for the corresponding mode. For uni-directional or bi-directional inter-prediction, for example, video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. Video encoder 200 may use similar modes to encode motion vectors for affine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of a block, video encoder 200 may calculate residual data for the block. The residual data, such as a residual block, represents sample by sample differences between the block and a prediction block for the block, formed using the corresponding prediction mode. Video encoder 200 may apply one or more transforms to the residual block, to produce transformed data in a transform domain instead of the sample domain. For example, video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data. Additionally, video encoder 200 may apply a secondary transform following the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like. Video encoder 200 produces transform coefficients following application of the one or more transforms.

As noted above, following any transforms to produce transform coefficients, video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the coefficients, providing further compression. By performing the quantization process, video encoder 200 may reduce the bit depth associated with some or all of the coefficients. For example, video encoder 200 may round an n-bit value down to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, video encoder 200 may perform a bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector. In some examples, video encoder 200 may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder 200 may perform an adaptive scan. After scanning the quantized transform coefficients to form the one-dimensional vector, video encoder 200 may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder 200 may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder 300 in decoding the video data.

To perform CABAC, video encoder 200 may assign a context within a context model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are zero-valued or not. The probability determination may be based on a context assigned to the symbol.

Video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to video decoder 300, e.g., in a picture header, a block header, a slice header, or other syntax data, such as a sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS). Video decoder 300 may likewise decode such syntax data to determine how to decode corresponding video data.

In this manner, video encoder 200 may generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks. Ultimately, video decoder 300 may receive the bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to that performed by video encoder 200 to decode the encoded video data of the bitstream. For example, video decoder 300 may decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder 200. The syntax elements may define partitioning information of a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantized transform coefficients. Video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block. Video decoder 300 uses a signaled prediction mode (intra- or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block. Video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. Video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information, such as syntax elements. The term “signaling” may generally refer to the communication of values syntax elements and/or other data used to decode encoded video data. That is, video encoder 200 may signal values for syntax elements in the bitstream. In general, signaling refers to generating a value in the bitstream. As noted above, source device 102 may transport the bitstream to destination device 116 substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device 112 for later retrieval by destination device 116.

FIGS. 2A and 2B are conceptual diagram illustrating an example quadtree binary tree (QTBT) structure 130, and a corresponding coding tree unit (CTU) 132. The solid lines represent quadtree splitting, and dotted lines indicate binary tree splitting. In each split (i.e., non-leaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where 0 indicates horizontal splitting and 1 indicates vertical splitting in this example. For the quadtree splitting, there is no need to indicate the splitting type, since quadtree nodes split a block horizontally and vertically into 4 sub-blocks with equal size. Accordingly, video encoder 200 may encode, and video decoder 300 may decode, syntax elements (such as splitting information) for a region tree level of QTBT structure 130 (i.e., the solid lines) and syntax elements (such as splitting information) for a prediction tree level of QTBT structure 130 (i.e., the dashed lines). Video encoder 200 may encode, and video decoder 300 may decode, video data, such as prediction and transform data, for CUs represented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parameters defining sizes of blocks corresponding to nodes of QTBT structure 130 at the first and second levels. These parameters may include a CTU size (representing a size of CTU 132 in samples), a minimum quadtree size (MinQTSize, representing a minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, representing a maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, representing a maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, representing the minimum allowed binary tree leaf node size).

The root node of a QTBT structure corresponding to a CTU may have four child nodes at the first level of the QTBT structure, each of which may be partitioned according to quadtree partitioning. That is, nodes of the first level are either leaf nodes (having no child nodes) or have four child nodes. The example of QTBT structure 130 represents such nodes as including the parent node and child nodes having solid lines for branches. If nodes of the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), they can be further partitioned by respective binary trees. The binary tree splitting of one node can be iterated until the nodes resulting from the split reach the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of QTBT structure 130 represents such nodes as having dashed lines for branches. The binary tree leaf node is referred to as a coding unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transform, without any further partitioning. As discussed above, CUs may also be referred to as “video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is set as 128×128 (luma samples and two corresponding 64×64 chroma samples), the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, the MinBTSize (for both width and height) is set as 4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to the CTU first to generate quad-tree leaf nodes. The quadtree leaf nodes may have a size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If the leaf quadtree node is 128×128, it will not be further split by the binary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in this example). Otherwise, the leaf quadtree node will be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (4, in this example), no further splitting is permitted. When the binary tree node has width equal to MinBTSize (4, in this example), it implies no further horizontal splitting is permitted. Similarly, a binary tree node having a height equal to MinBTSize implies no further vertical splitting is permitted for that binary tree node. As noted above, leaf nodes of the binary tree are referred to as CUs, and are further processed according to prediction and transform without further partitioning.

In this section video coding standards, especially motion vector prediction related techniques of previous standards, are discussed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions. The latest joint draft of MVC is described in “Advanced video coding for generic audiovisual services,” ITU-T Recommendation H.264, March 2010.

In addition, there is a newly developed video coding standard, namely High Efficiency Video Coding (HEVC), developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). A recent draft of HEVC is available from http://phenix.int-evry.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v34.zip.

Motion Information

For each block, a set of motion information can be available. The set of motion information contains motion information for forward and backward prediction directions. Here forward and backward prediction directions are two prediction directions corresponding to reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1) of a current picture or slice. The terms “forward” and “backward” do not necessarily have a geometry meaning. Instead, they are used to distinguish which reference picture list a motion vector is based on. Forward prediction means the prediction formed based on reference list 0, while backward prediction means the prediction formed based on reference list 1. In case both reference list 0 and reference list 1 are used to form a prediction for a given block, it is called bi-directional prediction.

For a given picture or slice, if only one reference picture list is used, every block inside the picture or slice is forward predicted. If both reference picture lists are used for a given picture or slice, a block inside the picture or slice may be forward predicted, or backward predicted, or bi-directionally predicted.

For each prediction direction, the motion information contains a reference index and a motion vector. A reference index is used to identify a reference picture in the corresponding reference picture list (e.g. RefPicList0 or RefPicList1). A motion vector has both a horizontal and a vertical component, with each indicating an offset value along horizontal and vertical direction respectively. In some descriptions, for simplicity, the word of “motion vector” may be used interchangeably with motion information, to indicate both the motion vector and its associated reference index.

POC

Picture order count (POC) is used in video coding standards to identify a display order of a picture. Although there are cases two pictures within one coded video sequence may have the same POC value, it typically doesn't happen within a coded video sequence. When multiple coded video sequences are present in a bitstream, pictures with a same value of POC may be closer to each other in terms of decoding order.

POC values of pictures are typically used for reference picture list construction, derivation of reference picture set as in HEVC and motion vector scaling.

Prediction Unit

A prediction unit (PU) refer to a basic unit of samples that share the same prediction information. In the inter prediction PU, the prediction information can be the same set of motion information or the same method to derive the motion information for the PU. In one example, PU can be the same as in HEVC block structure, and also can be the basic block in other block partitioning structures, quad-tree plus binary-tree partitioning, multi-type-tree partitioning, et al.

A sub-PU is a sub-block in a PU, in which the samples share the same set of motion information. In sub-PU level motion, the samples in a PU share the same method/model for motion information derivation, but a sub-PU can have its own set of motion information and may be different from other sub-PU in the same PU.

FIG. 3 illustrates an example flow chart of motion vector predictor derivation, as discussed herein. Two lists of motion vector predictor candidates are derived from the information of neighboring blocks in three-dimensional domain. The decoder adaptively chooses a list according to a decoded syntax element is_sub_pu_motion_flag from the bitstream.

In one example, sub_pu list may only exist if current block is larger than a predefined value. In another example, a block may contain only a subPU, e.g. 4×4 block, the flag is then to indicate motion information generation is based on subPU method or not. The two lists may include different number of motion prediction candidates, which may be predefined or signaled in SPS, PPS or slice header. The neighboring blocks could be the spatial neighbors in the current picture or the temporal neighbors in previous coded pictures.

As illustrated in FIG. 3, the derivation process of the two lists will be discussed. In 300, the decoder determines whether the flag is active or not. If the decoder determines the flag is not active, the decoder proceeds to 302. If the flag is active, the decoder proceeds to 306.

In 302, a first list of PU level motion prediction candidates are derived. In 306, a second list of sub-PU level motion prediction candidates are derived. PU level motion prediction candidate means all the pixels in the same PU share the same set of motion information. Sub-PU level motion prediction candidate means all the pixels in the same sub-PU share the same set of motion information, but different sub-PU in a PU may have different sets of motion information. A set of motion information can include inter-prediction direction, reference picture index or indices if using multiple references, motion vector or motion vectors if using multiple references.

An example of PU level motion vector candidates list is the HEVC merge candidates list. Examples of sub-PU level motion prediction include, but are not limited to, affine motion vector prediction (Affine), Alternative Temporal Motion Vector Prediction (ATMVP), Spatial-Temporal Motion Vector Prediction (STMVP), planar motion vector prediction, and Pattern Matched Motion Vector Derivation (PMVD), et al. An exemplary syntax table is shown in Table 1 below. The syntax element sub_pu_motion_idx may be used to indicate the selected candidate in the sub-PU level motion prediction candidate list, and the syntax element pu_motion_idx is used to indicate the selected candidate in the PU level motion prediction candidate list.

TABLE 1 Descriptor is_sub_pu_motion_flag ae(v) if is_sub_pu_motion_flag {  sub_pu_motion_idx ae(v) } else {  pu_motion_idx ae(v) }

In another method, PU level motion vector candidates may be divided into two groups. is_sub_pu_motion_flag is signaled when decoder receives syntax indicating that the selected candidate is not in the first group of PU level motion information candidates. The is_sub_pu_motion_flag may be implicitly signaled in PU level merge index as one of the indices. Then sub-PU level merge index would be further signaled if is_sub_pu_motion_flag is true. In one example, the PU level motion prediction candidates list insertion order is A→B→S→C→D→E. A, B, C, D, E denote the PU level motion prediction candidates, and S is an indicator of sub_pu_motion_flag. If S is selected, then sub_pu_motion_flag is inferred to be true. One example of A can be the left-bottom spatial merge candidate, and one example of B can be the top-right spatial merge candidate. Note that other insertion order may also be applied.

Note that the sub-PU level motion prediction candidates are grouped in all the methods described above.

Signaling for Motion Vector Prediction Candidate Selection

A syntax element is_sub_pu_motion_flag is firstly used to indicate whether the motion prediction candidate is sub-PU level. The is_sub_pu_motion_flag can be binarized using one bin (0/1) and coded by context based binary arithmetic coder. The context can be depending on the PU size/area or the PU depth in the block partitioning tree. A larger PU may tend to have more frequent in choosing sub-PU level motion vector prediction than smaller PU. The context can also depend on the sub_pu_motion_flag from spatial/temporal neighboring blocks. The chance of current PU use sub-PU motion is higher if neighboring blocks have sub-PU motion.

If is_sub_pu_motion_flag is true (“1”), a syntax element sub_pu_motion_idx is used to indicate the method to derive the sub-PU motion prediction candidate. The total number of methods, i.e. total number of sub-PU level motion prediction candidates, num_sub_pu motion can be signaled in high level syntax. The sub_pu_motion_idx can be binarized using truncated unary code depending on the num_sub_pu motion. However, other binarization method can also be applied.

If is_sub_pu_motion_flag is false (“0”), a syntax element nor_pu_motion_idx is used to indidate the method to derive the PU level motion prediction candidate. The total number of PU level motion vector prediction candidates, num_nor_pu motion can be signaled in high level syntax. The nor_pu_motion_idx can be binarized using truncated unary code depending on the num_nor_pu motion. However, other binarization method can also be applied.

Derivation of PU Level Motion Prediction Candidates

PU level motion prediction candidate can be derived from the spatial or temporal neighboring coded blocks similarly in HEVC. In HEVC merge mode,

In HEVC, the MV candidate list contains up to 5 candidates for the merge mode and only two candidates for the AMVP mode. A merge candidate may contain a set of motion information, e.g., motion vectors corresponding to both reference picture lists (list 0 and list 1) and the reference indices. If a merge candidate is identified by a merge index, the reference pictures used for the prediction of the current blocks, as well as the associated motion vectors are determined.

Based on the above, one or more motion vector predictors are selected based on a decoded candidate index.

In HEVC merge mode, up to four spatial MV candidates 402, 404, 406, and 408 of a block 400 can be derived with the orders shown in FIG. 4. The order is the following: left (0, A1), above (1, B1), above right (2, B0), below left (3, A0), and above left (4, B2).

Temporal neighboring candidates in HEVC will now be discussed. A Temporal motion vector predictor (TMVP) candidate, if enabled and available, is added into the MV candidate list after spatial motion vector candidates. The primary block location for TMVP candidate derivation is the bottom right block outside of the collocated PU as shown in Error! Reference source not found.5 as a block “T” 500, to compensate the bias to the above and left blocks used to generate spatial neighboring candidates. However, if that block 502 is located outside of the current CTB row or motion information is not available, the block is substituted with a center block 504 of the PU. Motion vector for TMVP candidate is derived from the co-located PU of the co-located picture, indicated in the slice level. The motion vector for the co-located PU is called collocated MV.

Derivation of Sub-PU Level Motion Prediction Candidates

The sub-PU level motion prediction candidates can include, but not limit to, affine motion prediction, Alternative Temporal Motion Vector Prediction (ATMVP), Spatial-Temporal Motion Vector Prediction (STMVP), planar motion vector prediction, Pattern Matched Motion Vector Derivation (PMVD), et al. In the following, we will illustrate examples of these sub-PU level motion prediction. However, some variations or other sub-PU level motion prediction can also be added.

Affine Motion Prediction

In 4-parameter affine motion prediction method, the motion vector field of a block is described by equation (1):

$\begin{matrix} \left\{ \begin{matrix} {v_{x} = {{\frac{v_{1x} - v_{0x}}{w}x} - {\frac{v_{1y} - v_{0y}}{h}y} + v_{0x}}} \\ {v_{y} = {{\frac{v_{1y} - v_{0y}}{w}x} - {\frac{v_{1x} - v_{0x}}{h}y} + v_{0y}}} \end{matrix} \right. & (1) \end{matrix}$

where (w,h) is the size of the block, and (x,y) is the coordinate. (v_(0x), v_(0y)) is the motion vector of the top-left corner control point, and (v_(1x), v_(1y)) is the motion vector of the top-right corner control point.

In 6-parameter affine motion prediction method, the motion field of a block is described by equation (2):

$\begin{matrix} \left\{ \begin{matrix} {v_{x} = {{\frac{v_{1x} - v_{0x}}{w}x} - {\frac{v_{2x} - v_{0x}}{h}y} + v_{0x}}} \\ {v_{y} = {{\frac{v_{1y} - v_{0y}}{w}x} - {\frac{v_{2y} - v_{0y}}{h}y} + v_{0y}}} \end{matrix} \right. & (2) \end{matrix}$

-   -   where in addition, (v_(2x), v_(2y)) is the motion vector of the         bottom-left corner control point.

In sub-PU based affine motion prediction, the MV of a sub-PU can be derived by calculating the MV at the center of the sub-PU. Alternatively, we can scaled down (w,h) and (x,y) according to the size of sub-PU.

In one method, (v_(ix), v_(iy)) can be derived from a neighboring block that is previously coded by affine motion, considering that the current block shares the same affine motion model with the previous coded neighboring block.

In another method, (v_(ix), v_(iy)) can be derived by the motion vector at a neighboring coded block. For example, as shown in FIG. 6, (v_(0x), v_(0y)) can be derived from motion vector at block A 600, B 602, or C 604, (v_(1x), v_(1y)) can be derived from motion vector at block C 606 or D 608, (v_(2x), v_(2y)) can be derived from block E 610 or F 612.

Alternative Temporal Motion Vector Prediction

In the alternative temporal motion vector prediction (ATMVP) method (or sometime called advanced temporal motion vector prediction), the temporal motion vector prediction (TMVP) is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from sub-PUs of the current PU.

Spatial-Temporal Motion Vector Prediction

In the spatial-temporal motion vector prediction method, the motion vectors of sub-PUs are derived recursively, following raster scan order. FIG. 7 illustrate the concept of STMVP. Consider a 8×8 PU which contains four 4×4 sub-PUs A, B, C, and D. The neighbouring 4×4 blocks in current frame are labelled as a, b, c, and d. The motion derivation for sub-CU A starts by identifying its two spatial neighbours. The first neighbour is the N×N block above sub-CU A (block c). If this block c is not available or is intra coded the other N×N blocks above sub-CU A are checked (from left to right, starting at block c). The second neighbour is a block to the left of the sub-CU A (block b). If block b is not available or is intra coded other blocks to the left of sub-CU A are checked (from top to bottom, staring at block b). The motion information obtained from the neighbouring blocks for each list is scaled to the first reference frame for a given list. Next, temporal motion vector predictor (TMVP) of sub-block A is derived by following the same procedure of TMVP derivation as specified in HEVC. The motion information of the collocated block at location D is fetched and scaled accordingly. Finally, after retrieving and scaling the motion information, all available motion vectors (up to 3) are averaged separately for each reference list. The averaged motion vector is assigned as the motion vector of the current sub-CU.

Pattern Matched Motion Vector Derivation

The Pattern matched motion vector derivation (PMMVD) method is based on frame-rate up conversion techniques. Motion derivation process has two steps. A PU-level motion search is first performed, then followed by a Sub-PU level motion refinement. At PU level, an initial motion vector is derived for the whole PU based on bilateral matching or template matching. First, a list of MV candidates is generated and the candidate which leads to the minimum matching cost is selected as the starting point for further PU level refinement. Then a local search based on bilateral matching or template matching around the starting point is performed and the MV results in the minimum matching cost is taken as the MV for the whole CU. Subsequently, the motion information is further refined at sub-PU level with the derived CU motion vectors as the starting points.

The concept of bilateral matching is illustrated in Error! Reference source not found.8. The bilateral matching is used to derive motion information by finding the closest match between two blocks along the motion trajectory of the current block in two different reference pictures. Under the assumption of continuous motion trajectory, the motion vectors MV0 and MV1 pointing to the two reference blocks shall be proportional to the temporal distances, i.e., TD0 and TD1, between the current picture and the two reference pictures. As a special case, when the current picture is temporally between the two reference pictures and the temporal distance from the current picture to the two reference pictures is the same, the bilateral matching becomes mirror based bi-directional MV.

Template match as illustrated in Error! Reference source not found.9 is used to derive motion information by finding the closest match between a template (top and/or left neighbouring blocks of the current block) in the current picture and a block (same size to the template) in a reference picture.

Planar Motion Vector Prediction

Planar motion vector prediction is achieved by averaging a horizontal and vertical linear interpolation on 4×4 block basis as follows.

P(x,y)=(H×P _(h)(x,y)+W×P _(v)(x,y)+H×W)/(2×H×W)

W and H denote the width and the height of the block. (x,y) is the coordinates of current sub-block relative to the above left corner sub-block. All the distances are denoted by the pixel distances divided by 4. P(x,y) is the motion vector of current sub-block.

The horizontal prediction p_(h)(x,y) and the vertical prediction p_(v)(x,y) for location (x,y) are calculated as follows:

P _(h)(x,y)=(W−1−x)×L(−1,y)+(x+1)×R(W,y)

P _(v)(x,y)=(H−1−y)×A(x,−1)+(y+1)×B(x,H)

-   -   where L(−1,y) and R(W,y) are the motion vectors of the 4×4         blocks to the left and right of the current block. A(x,−1) and B         (x,H) are the motion vectors of the 4×4 blocks to the above and         bottom of the current block, as shown in Error! Reference source         not found.9.

The reference motion information of the left column and above row neighbour blocks are derived from the spatial neighbour blocks of current block.

The reference motion information of the right column and bottom row neighbour blocks are derived as follows.

-   1) Derive the motion information of the bottom right temporal     neighbour 4×4 block -   2) Compute the motion vectors of the right column neighbour 4×4     blocks, using the derived motion information of the bottom right     neighbour 4×4 block along with the motion information of the above     right neighbour 4×4 block, as R(W,y)=((H−y−1)×AR+(y+1)×BR)/H. -   3) Compute the motion vectors of the bottom row neighbour 4×4     blocks, using the derived motion information of the bottom right     neighbour 4×4 block along with the motion information of the bottom     left neighbour 4×4 block, as B(x,H)=((W−x−1)×BL+(x+1)×BR)/W.     -   where AR is the motion vector of the above right spatial         neighbour 4×4 block, BR is the motion vector of the bottom right         temporal neighbour 4×4 block, and BL is the motion vector of the         bottom left spatial neighbour 4×4 block, as shown in Error!         Reference source not found.10.

The motion information obtained from the neighbouring blocks for each list is scaled to the first reference picture for a given list.

Candidate List Insertion

If available, the sub-PU level motion prediction candidates are inserted in the list in the following default order: Affine→ATMVP→STMVP→PMMVD→Planar. The default order may be predefined or signaled based on slice type, temporal layer, affine motion model, and/or availability of temporal motion predictor. The default order may also differ based on block type, block shape, or block size. The maximum number of sub-PU level motion prediction candidates is determined by a predefined number and/or the total number of available sub-PU level motion prediction candidates as indicated by high level syntax. In one example, if the predefined number is 3, and all of the affine, ATMVP, STMVP, PMMVD, and Planar candidates are available, then the maximum number is 3. But if only the affine and ATMVP are available, then the maximum number is 2. If the maximum number is 0, then the is_sub_pu_motion_flag is inferred to be false (‘0’) and is not signaled in the bitstream. Other default candidate order can also be used.

In one example, Affine→PMMVD→ATMVP→STMVP→Planar.

In another example, PMMVD→Affine→ATMVP→STMVP→Planar.

In another example, two or more affine candidates may be used.

Affine1→Affine 2→PMMVD→ATMVP→STMVP→Planar

Or Affine1→ATMVP→Affine 2→Planar

Prioritized Candidate Reorder

The default sub-PU level motion prediction candidates list can be reordered based on their occurrences in the neighboring coded blocks. In one example the candidate that has more occurrences in the neighboring coded blocks is put in a lower index position in the list.

Partial Prioritized Candidate Reorder

In order to reduce the complexity of reordering of candidates, the prioritized candidate reorder is only applied to one or multiple sub-lists. For example, candidate 1-2, 3-4 in the default order are reordered separately based on their appearance in the neighboring coded blocks.

Pruning

To reduce the complexity, no pruning or partial pruning may be applied in the sub-PU candidate list. In one example, pruning between ATMVP, STMVP, and planar may be applied, but no pruning is applied between affine and the rest of sub-PU candidates.

In another example, pruning is only applied to the number of sub-PU is smaller or equal to a predefined value.

Alternative Signaling Methods of Sub-PU Motion Prediction Candidate

The selection of sub-PU motion prediction candidate can be signaled by enabling flags according to the candidate insertion order instead of an index. In one example, if the insertion order is Affine→PMMVD→ATMVP→STMVP→Planar, then the signaling is as shown in Table 2.

In another alternative method, the sub-PU motion prediction candidates can be grouped in several sub-groups. For example, Affine, Planar are grouped into sub-group 1, ATMVP and STMVP are grouped into sub-group 2, and PMMVD is yet another sub-group 3. An exemplary signaling is shown in Table 3. A syntax pmmvd_flag is first signaled to indicate whether it's PMMVD candidate or not. Then if it's not PMMVD candidate, another syntax element sub_group1 flag is signaled to indicate whether it's sub-group 1 candidates. If sub_group1 flag is true indicating it's sub-group 1 candidates, affine_flag is sginaled to indicate whether it's Affine candidate. If it's not affine candidate, then planar_mv_flag is set as true to indicate it's Planar candidate. If sub_group1 flag is false, then atmvp_flag is signaled to indicate whether it's ATMVP candidate. If it's not ATMVP candidate, stmvp_flag is set as true to indicate it's STMVP candidate.

TABLE 2 Descriptor affine_flag ae(v) if(!affine_flag) {  pmmvd_flag ae(v)  if(!pmmd_flag) {  atmvp_flag ae(v)  if(!atmvp_flag) {   stmvp_flag ae(v)   if(!stmvp_flag) {   planar_mv_flag = true   }  }  } }

TABLE 3 Descriptor pmmvd_flag ae(v) if(!pmmvd_flag) {  sub_group1_flag ae(v)  if(sub_group1_flag) {  affine_flag ae(v)  if(!affine_flag) {   planar_mv_flag = true  }  } else {  atmvp_flag ae(v)  if(!atmvp_flag) {   stmvp_flag = true  }  } }

Note that in Table 2 and Table 3, availability check ignored for easy exemplary. A flag is inferred to be false (‘0’) if the corresponding candidate is not available. Also note that other variations of grouping can also be applied.

FIG. 11 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. FIG. 11 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 200 in the context of video coding standards such as the HEVC video coding standard and the H.266 video coding standard in development. However, the techniques of this disclosure are not limited to these video coding standards, and are applicable generally to video encoding and decoding.

In the example of FIG. 11, video encoder 200 includes video data memory 230, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 202, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, decoded picture buffer (DPB) 218, and entropy encoding unit 220.

Video data memory 230 may store video data to be encoded by the components of video encoder 200. Video encoder 200 may receive the video data stored in video data memory 230 from, for example, video source 104 (FIG. 1). DPB 218 may act as a reference picture memory that stores reference video data for use in prediction of subsequent video data by video encoder 200. Video data memory 230 and DPB 218 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 230 and DPB 218 may be provided by the same memory device or separate memory devices. In various examples, video data memory 230 may be on-chip with other components of video encoder 200, as illustrated, or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not be interpreted as being limited to memory internal to video encoder 200, unless specifically described as such, or memory external to video encoder 200, unless specifically described as such. Rather, reference to video data memory 230 should be understood as reference memory that stores video data that video encoder 200 receives for encoding (e.g., video data for a current block that is to be encoded). Memory 106 of FIG. 1 may also provide temporary storage of outputs from the various units of video encoder 200.

The various units of FIG. 11 are illustrated to assist with understanding the operations performed by video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, the one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and/or programmable cores, formed from programmable circuits. In examples where the operations of video encoder 200 are performed using software executed by the programmable circuits, memory 106 (FIG. 1) may store the object code of the software that video encoder 200 receives and executes, or another memory within video encoder 200 (not shown) may store such instructions.

Video data memory 230 is configured to store received video data. Video encoder 200 may retrieve a picture of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202. Video data in video data memory 230 may be raw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motion compensation unit 224, and an intra-prediction unit 226. Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes. As examples, mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit 222 and/or motion compensation unit 224), an affine unit, a linear model (LM) unit, or the like.

Mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters may include partitioning of CTUs into CUs, prediction modes for the CUs, transform types for residual data of the CUs, quantization parameters for residual data of the CUs, and so on. Mode selection unit 202 may ultimately select the combination of encoding parameters having rate-distortion values that are better than the other tested combinations.

Video encoder 200 may partition a picture retrieved from video data memory 230 into a series of CTUs, and encapsulate one or more CTUs within a slice. Mode selection unit 210 may partition a CTU of the picture in accordance with a tree structure, such as the QTBT structure or the quad-tree structure of HEVC described above. As described above, video encoder 200 may form one or more CUs from partitioning a CTU according to the tree structure. Such a CU may also be referred to generally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or in HEVC, the overlapping portion of a PU and a TU). For inter-prediction of a current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB 218). In particular, motion estimation unit 222 may calculate a value representative of how similar a potential reference block is to the current block, e.g., according to sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or the like. Motion estimation unit 222 may generally perform these calculations using sample-by-sample differences between the current block and the reference block being considered. Motion estimation unit 222 may identify a reference block having a lowest value resulting from these calculations, indicating a reference block that most closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for uni-directional inter-prediction, motion estimation unit 222 may provide a single motion vector, whereas for bi-directional inter-prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then generate a prediction block using the motion vectors. For example, motion compensation unit 224 may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit 224 may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data, e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding, intra-prediction unit 226 may generate the prediction block from samples neighboring the current block. For example, for directional modes, intra-prediction unit 226 may generally mathematically combine values of neighboring samples and populate these calculated values in the defined direction across the current block to produce the prediction block. As another example, for DC mode, intra-prediction unit 226 may calculate an average of the neighboring samples to the current block and generate the prediction block to include this resulting average for each sample of the prediction block.

Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives a raw, uncoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block. In some examples, residual generation unit 204 may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, each PU may be associated with a luma prediction unit and corresponding chroma prediction units. Video encoder 200 and video decoder 300 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, video encoder 200 may support PU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder 200 and video decoder 300 may also support asymmetric partitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition a CU into PUs, each CU may be associated with a luma coding block and corresponding chroma coding blocks. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder 200 and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as few examples, mode selection unit 202, via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 to be encoded.

As described above, residual generation unit 204 receives the video data for the current block and the corresponding prediction block. Residual generation unit 204 then generates a residual block for the current block. To generate the residual block, residual generation unit 204 calculates sample-by-sample differences between the prediction block and the current block. Thus,

Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to a residual block. In some examples, transform processing unit 206 may perform multiple transforms to a residual block, e.g., a primary transform and a secondary transform, such as a rotational transform. In some examples, transform processing unit 206 does not apply transforms to a residual block.

Quantization unit 208 may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit 208 may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode selection unit 202) may adjust the degree of quantization applied to the coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit 206.

Inverse quantization unit 210 and inverse transform processing unit 212 may apply inverse quantization and inverse transforms to a quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block. Reconstruction unit 214 may produce a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and a prediction block generated by mode selection unit 202. For example, reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit 202 to produce the reconstructed block.

Filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance, in examples where operations of filter unit 216 are not needed, reconstruction unit 216 may store reconstructed blocks to DPB 218. In examples where operations of filter unit 224 are needed, filter unit 216 may store the filtered reconstructed blocks to DPB 218. Motion estimation unit 222 and motion compensation unit 224 may retrieve a reference picture from DPB 218, formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures. In addition, intra-prediction unit 226 may use reconstructed blocks in DPB 218 of a current picture to intra-predict other blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy encoding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy encoding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit 202. Entropy encoding unit 220 may perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to generate entropy-encoded data. For example, entropy encoding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data. In some examples, entropy encoding unit 220 may operate in bypass mode where syntax elements are not entropy encoded.

Video encoder 200 may output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture. In particular, entropy encoding unit 220 may output the bitstream

The operations described above are described with respect to a block. Such description should be understood as being operations for a luma coding block and/or chroma coding blocks. As described above, in some examples, the luma coding block and chroma coding blocks are luma and chroma components of a CU. In some examples, the luma coding block and the chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks. As one example, operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the reference picture may be the same. As another example, the intra-prediction process may be the same for the luma coding blocks and the chroma coding blocks.

Video encoder 200 represents an example of a device configured to encode video data including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to derive a frame rate up conversion (FRUC) template using prediction pixel value and perform a decoder-side motion vector derivation technique using the derived template. In another example, video decoder 300 may be configured to determine respective motion vectors from one or more neighboring blocks of video data and derive a motion vector for a current block of video data using the respective motion vectors from the one or more neighboring blocks of video data. In another example, video decoder 300 may be configured to determine respective motion vectors from one or more collocated blocks of video data, and derive a motion vector for a current block of video data using the respective motion vectors from the one or more collocated blocks of video data.

FIG. 12 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. FIG. 12 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video decoder 300 is described according to the techniques of JEM,H.266/VVC, and HEVC. However, the techniques of this disclosure may be performed by video coding devices that are configured to other video coding standards.

In the example of FIG. 12, video decoder 300 includes coded picture buffer (CPB) memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and decoded picture buffer (DPB) 314. Prediction processing unit 304 includes motion compensation unit 316 and intra-prediction unit 318. Prediction processing unit 304 may include addition units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit 316), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder 300 may include more, fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder 300. The video data stored in CPB memory 320 may be obtained, for example, from computer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, CPB memory 320 may store video data other than syntax elements of a coded picture, such as temporary data representing outputs from the various units of video decoder 300. DPB 314 generally stores decoded pictures, which video decoder 300 may output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory 320 and DPB 314 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, CPB memory 320 may be on-chip with other components of video decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 may retrieve coded video data from memory 120 (FIG. 1). That is, memory 120 may store data as discussed above with CPB memory 320. Likewise, memory 120 may store instructions to be executed by video decoder 300, when some or all of the functionality of video decoder 300 is implemented in software to executed by processing circuitry of video decoder 300.

The various units shown in FIG. 12 are illustrated to assist with understanding the operations performed by video decoder 300. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to FIG. 11, fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, the one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, the one or more units may be integrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analog circuits, and/or programmable cores formed from programmable circuits. In examples where the operations of video decoder 300 are performed by software executing on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software that video decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPB and entropy decode the video data to reproduce syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-block basis. Video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, i.e., decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and/or transform mode indication(s). Inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 306 to apply. Inverse quantization unit 306 may, for example, perform a bitwise left-shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 may thereby form a transform coefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.

Furthermore, prediction processing unit 304 generates a prediction block according to prediction information syntax elements that were entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 may generate the prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB 314 from which to retrieve a reference block, as well as a motion vector identifying a location of the reference block in the reference picture relative to the location of the current block in the current picture. Motion compensation unit 316 may generally perform the inter-prediction process in a manner that is substantially similar to that described with respect to motion compensation unit 224 (FIG. 11).

As another example, if the prediction information syntax elements indicate that the current block is intra-predicted, intra-prediction unit 318 may generate the prediction block according to an intra-prediction mode indicated by the prediction information syntax elements. Again, intra-prediction unit 318 may generally perform the intra-prediction process in a manner that is substantially similar to that described with respect to intra-prediction unit 226 (FIG. 11). Intra-prediction unit 318 may retrieve data of neighboring samples to the current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations on reconstructed blocks. For example, filter unit 312 may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit 312 are not necessarily performed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. As discussed above, DPB 314 may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent motion compensation, to prediction processing unit 304. Moreover, video decoder 300 may output decoded pictures from DPB for subsequent presentation on a display device, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a video decoding device including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to implement the methods and processes discussed herein.

For example, the encoded video data may include the following syntax:

TABLE 4 Merge Data Syntax merge_data( x0, y0, cbWidth, cbHeight ) { Descriptor  mmvd_flag[ x0 ][ y0 ] ae(v)  if( mmvd_flag[ x0 ][ y0 ] == 1 ) {   mmvd_merge_flag[ x0 ][ y0 ] ae(v)   mmvd_distance_idx[ x0 ][ y0 ] ae(v)   mmvd_direction_idx[ x0 ][ y0 ] ae(v)  } else {   if( MaxNumSubblockMergeCand > 0 && cbWidth >= 8 && cbHeight >= 8 )    merge_subblock_flag[ x0 ][ y0 ] ae(v)   if( merge_subblock_flag[ x0 ][ y0 ] == 1 ) {    if( MaxNumSubblockMergeCand > 1 )     merge_subblock_idx[ x0 ][ y0 ] ae(v)   } else {    if( sps_ciip_enabled_flag && cu_skip_flag[ x0 ][ y0 ] == 0 &&     ( cbWidth * cbHeight) >= 64 && cbWidth < 128 && cbHeight < 128 ) {     ciip_flag[ x0 ][ y0 ] ae(v)     if( ciip_flag[ x0 ][ y0 ] ) {      if ( cbWidth <= 2 * cbHeight || cbHeight <= 2 * cbWidth )       ciip_luma_mpm_flag[ x0 ][ y0 ] ae(v)      if( ciip_luma_mpm_flag[ x0 ][ y0 ] )       ciip_luma_mpm_idx[ x0 ][ y0 ] ae(v)     }    }    if( sps_triangle_enabled_flag && tile_group_type == B &&         cbWidth * cbHeight >= 64)     merge_triangle_flag[ x0 ][ y0 ] ae(v)    if( merge_triangle_flag[ x0 ][ y0 ] )     merge_triangle_idx[ x0 ][ y0 ] ae(v)    else if( MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)   }  } }

merge_subblock_flag[x0][y0] specifies whether the subblock-based inter prediction parameters for the current coding unit are inferred from neighbouring blocks. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. When merge_subblock_flag[x0][y0] is not present, it is inferred to be equal to 0.

merge_subblock_idx[x0][y0] specifies the merging candidate index of the subblock-based merging candidate list where x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.

When merge_subblock_idx[x0][y0] is not present, it is inferred to be equal to 0.

If merge_subblock_flag[xCb][yCb] is equal to 1, the derivation process for motion vectors and reference indices in subblock merge mode as specified in Error! Reference source not found. is invoked with the luma coding block location (xCb, yCb), the luma coding block width cbWidth and the luma coding block height cbHeight as inputs, the number of luma coding subblocks in horizontal direction numSbX and in vertical direction numSbY, the reference indices refIdxL0, refIdxL1, the prediction list utilization flag arrays predFlagL0[xSbIdx][ySbIdx] and predFlagL1[xSbIdx][ySbIdx], the luma subblock motion vector arrays mvL0[xSbIdx][ySbIdx] and mvL0[xSbIdx][ySbIdx], and the chroma subblock motion vector arrays mvCL0[xSbIdx][ySbIdx] and mvCL1[xSbIdx][ySbIdx], with xSbIdx=0 . . . numSbX−1, ySbIdx=0 . . . numSbY−1, and the bi-prediction weight index gbiIdx as outputs.

It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples are within the scope of the following claims. 

What is claimed is:
 1. A method of decoding video data, the method comprising: receiving encoded video data; parsing a sub-prediction unit motion flag from the encoded video data; in response to determining the sub-prediction unit motion flag is active, deriving a list of sub-prediction unit level motion prediction candidates; in response to determining the sub-prediction unit motion flag is not active, deriving a list of prediction unit level motion prediction candidates; selecting a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates; and decoding the encoded video data using the selected motion vector predictor.
 2. The method of claim 1, wherein the encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block.
 3. The method of claim 2, wherein the neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture.
 4. The method of claim 2, wherein the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks.
 5. The method of claim 1, wherein pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor.
 6. The method of claim 1, wherein the prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates.
 7. The method of claim 1, wherein the list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD).
 8. The method of claim 1, further comprising: deriving a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.
 9. An apparatus for decoding video data, the apparatus comprising: a memory for storing a received encoded video data; and a processor, the processor configured to, parse a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, derive a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, derive a list of prediction unit level motion prediction candidates, select a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decode the encoded video data using the selected motion vector predictor.
 10. The apparatus of claim 9, wherein the encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block.
 11. The apparatus of claim 10, wherein the neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture.
 12. The apparatus of claim 10, wherein the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks.
 13. The apparatus of claim 9, wherein pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor.
 14. The apparatus of claim 9, wherein the prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates.
 15. The apparatus of claim 9, wherein the list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD).
 16. The apparatus of claim 9, the processor further configured to, derive a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.
 17. An apparatus for decoding video data, the apparatus comprising: a memory means for storing a received encoded video data; and a processor means, the processor means configured to, parse a sub-prediction unit motion flag from the encoded video data, in response to determining the sub-prediction unit motion flag is active, derive a list of sub-prediction unit level motion prediction candidates, in response to determining the sub-prediction unit motion flag is not active, derive a list of prediction unit level motion prediction candidates, select a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates, and decode the encoded video data using the selected motion vector predictor.
 18. The apparatus of claim 17, wherein the encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block.
 19. The apparatus of claim 18, wherein the neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture.
 20. The apparatus of claim 18, wherein the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks.
 21. The apparatus of claim 17, wherein pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor.
 22. The apparatus of claim 17, wherein the prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates.
 23. The apparatus of claim 17, wherein the list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD).
 24. The apparatus of claim 17, the processor means further configured to, derive a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected.
 25. A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform a method comprising: receiving encoded video data; parsing a sub-prediction unit motion flag from the encoded video data; in response to determining the sub-prediction unit motion flag is active, deriving a list of sub-prediction unit level motion prediction candidates; in response to determining the sub-prediction unit motion flag is not active, deriving a list of prediction unit level motion prediction candidates; selecting a motion vector predictor from either the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates; and decoding the encoded video data using the selected motion vector predictor.
 26. The medium of claim 25, wherein the encoded video data includes a current block and wherein the list of sub-prediction unit level motion prediction candidates and the list of prediction unit level motion prediction candidates are derived from neighboring blocks of the current block.
 27. The medium of claim 26, wherein the neighboring blocks are spatial neighbors of the current block in a current picture or temporal neighbors of the current block in a previously coded picture.
 28. The medium of claim 26, wherein the list of sub-prediction unit level motion prediction candidates or the list of prediction unit level motion prediction candidates is at least partially ordered based on motion prediction occurrences in the neighboring blocks.
 29. The medium of claim 25, wherein pixels in a prediction unit share first motion vector information and pixels in a sub-prediction unit share second motion vector information, and wherein the first motion vector information or the second vector information is determined from the selected motion vector predictor, wherein the prediction unit level motion vector candidates list including at least one of: spatial neighboring candidates and temporal neighboring candidates, and wherein the list of sub-prediction unit level motion prediction candidates includes at least one of: affine motion vector prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), planar motion vector prediction, and pattern matched motion vector derivation (PMVD).
 30. The medium of claim 25, the method further comprising: deriving a merging candidate index in response to determining the sub-prediction unit motion flag is active, wherein the merging candidate index specifies the motion vector predictor to be selected. 